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Ray PS, Sullivan JC, Jia J, Francis J, Finnerty JR, Fox PL. Evolution of function of a fused metazoan tRNA synthetase. Mol Biol Evol 2010; 28:437-47. [PMID: 20829344 DOI: 10.1093/molbev/msq246] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The origin and evolution of multidomain proteins are driven by diverse processes including fusion/fission, domain shuffling, and alternative splicing. The 20 aminoacyl-tRNA synthetases (AARS) constitute an ancient conserved family of multidomain proteins. The glutamyl-prolyl tRNA synthetase (EPRS) of bilaterian animals is unique among AARSs, containing two functional enzymes catalyzing ligation of glutamate and proline to their cognate transfer RNAs (tRNAs). The ERS and PRS catalytic domains in multiple bilaterian taxa are linked by variable number of helix-turn-helix domains referred to as WHEP-TRS domains. In addition to its canonical aminoacylation activities, human EPRS exhibits a noncanonical function as an inflammation-responsive regulator of translation. Recently, we have shown that the WHEP domains direct this auxiliary function of human EPRS by interacting with an mRNA stem-loop element (interferon-gamma-activated inhibitor of translation [GAIT] element). Here, we show that EPRS is present in the cnidarian Nematostella vectensis, which pushes the origin of the fused protein back to the cnidarian-bilaterian ancestor, 50-75 My before the origin of the Bilateria. Remarkably, the Nematostella EPRS mRNA is alternatively spliced to yield three isoforms with variable number and sequence of WHEP domains and with distinct RNA-binding activities. Whereas one isoform containing a single WHEP domain binds tRNA, a second binds both tRNA and GAIT element RNA. However, the third isoform contains two WHEP domains and like the human ortholog binds specifically to GAIT element RNA. These results suggest that alternative splicing of WHEP domains in the EPRS gene of the cnidarian-bilaterian ancestor gave rise to a novel molecular function of EPRS conserved during metazoan evolution.
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Affiliation(s)
- Partho Sarothi Ray
- Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, USA
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102
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Cho HH, Cahill CM, Vanderburg CR, Scherzer CR, Wang B, Huang X, Rogers JT. Selective translational control of the Alzheimer amyloid precursor protein transcript by iron regulatory protein-1. J Biol Chem 2010; 285:31217-32. [PMID: 20558735 DOI: 10.1074/jbc.m110.149161] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Iron influx increases the translation of the Alzheimer amyloid precursor protein (APP) via an iron-responsive element (IRE) RNA stem loop in its 5'-untranslated region. Equal modulated interaction of the iron regulatory proteins (IRP1 and IRP2) with canonical IREs controls iron-dependent translation of the ferritin subunits. However, our immunoprecipitation RT-PCR and RNA binding experiments demonstrated that IRP1, but not IRP2, selectively bound the APP IRE in human neural cells. This selective IRP1 interaction pattern was evident in human brain and blood tissue from normal and Alzheimer disease patients. We computer-predicted an optimal novel RNA stem loop structure for the human, rhesus monkey, and mouse APP IREs with reference to the canonical ferritin IREs but also the IREs encoded by erythroid heme biosynthetic aminolevulinate synthase and Hif-2α mRNAs, which preferentially bind IRP1. Selective 2'-hydroxyl acylation analyzed by primer extension analysis was consistent with a 13-base single-stranded terminal loop and a conserved GC-rich stem. Biotinylated RNA probes deleted of the conserved CAGA motif in the terminal loop did not bind to IRP1 relative to wild type probes and could no longer base pair to form a predicted AGA triloop. An AGU pseudo-triloop is key for IRP1 binding to the canonical ferritin IREs. RNA probes encoding the APP IRE stem loop exhibited the same high affinity binding to rhIRP1 as occurs for the H-ferritin IRE (35 pm). Intracellular iron chelation increased binding of IRP1 to the APP IRE, decreasing intracellular APP expression in SH-SY5Y cells. Functionally, shRNA knockdown of IRP1 caused increased expression of neural APP consistent with IRP1-APP IRE-driven translation.
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Affiliation(s)
- Hyun-Hee Cho
- Neurochemistry Laboratory, Department of Psychiatry-Neuroscience, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA
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103
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Hu YH, Zheng WJ, Sun L. Identification and molecular analysis of a ferritin subunit from red drum (Sciaenops ocellatus). FISH & SHELLFISH IMMUNOLOGY 2010; 28:678-686. [PMID: 20064620 DOI: 10.1016/j.fsi.2010.01.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2009] [Revised: 12/23/2009] [Accepted: 01/03/2010] [Indexed: 05/28/2023]
Abstract
Ferritin is a conserved iron binding protein existing ubiquitously in prokaryotes and eukaryotes. In this study, the gene encoding a ferritin M subunit homologue (SoFer1) was cloned from red drum (Sciaenops ocellatus) and analyzed at expression and functional levels. The open reading frame of SoFer1 is 531 bp and preceded by a 5'-untranslated region that contains a putative Iron Regulatory Element (IRE) preserved in many ferritins. The deduced amino acid sequence of SoFer1 possesses both the ferroxidase center of mammalian H ferritin and the iron nucleation site of mammalian L ferritin. Expression of SoFer1 was tissue specific and responded positively to experimental challenges with Gram-positive and Gram-negative fish pathogens. Treatment of red drum liver cells with iron, copper, and oxidant significantly upregulated the expression of SoFer1 in time-dependent manners. To further examine the potential role of SoFer1 in antioxidation, red drum liver cells transfected transiently with SoFer1 were prepared. Compared to control cells, SoFer1 transfectants exhibited reduced production of reactive oxygen species following H(2)O(2) challenge. Finally, to examine the iron binding potential of SoFer1, SoFer1 was expressed in and purified from Escherichia coli as a recombinant protein. Iron-chelating analysis showed that purified recombinant SoFer1 was capable of iron binding. Taken together, these results suggest that SoFer1 is likely to be a functional ferritin involved in iron sequestration, host immune defence against bacterial infection, and antioxidation.
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Affiliation(s)
- Yong-hua Hu
- Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, PR China
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104
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Goforth JB, Anderson SA, Nizzi CP, Eisenstein RS. Multiple determinants within iron-responsive elements dictate iron regulatory protein binding and regulatory hierarchy. RNA (NEW YORK, N.Y.) 2010; 16:154-69. [PMID: 19939970 PMCID: PMC2802025 DOI: 10.1261/rna.1857210] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Iron regulatory proteins (IRPs) are iron-regulated RNA binding proteins that, along with iron-responsive elements (IREs), control the translation of a diverse set of mRNA with 5' IRE. Dysregulation of IRP action causes disease with etiology that may reflect differential control of IRE-containing mRNA. IREs are defined by a conserved stem-loop structure including a midstem bulge at C8 and a terminal CAGUGH sequence that forms an AGU pseudo-triloop and N19 bulge. C8 and the pseudo-triloop nucleotides make the majority of the 22 identified bonds with IRP1. We show that IRP1 binds 5' IREs in a hierarchy extending over a ninefold range of affinities that encompasses changes in IRE binding affinity observed with human L-ferritin IRE mutants. The limits of this IRE binding hierarchy are predicted to arise due to small differences in binding energy (e.g., equivalent to one H-bond). We demonstrate that multiple regions of the IRE stem not predicted to contact IRP1 help establish the binding hierarchy with the sequence and structure of the C8 region displaying a major role. In contrast, base-pairing and stacking in the upper stem region proximal to the terminal loop had a minor role. Unexpectedly, an N20 bulge compensated for the lack of an N19 bulge, suggesting the existence of novel IREs. Taken together, we suggest that a regulatory binding hierarchy is established through the impact of the IRE stem on the strength, not the number, of bonds between C8 or pseudo-triloop nucleotides and IRP1 or through their impact on an induced fit mechanism of binding.
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Affiliation(s)
- Jeremy B Goforth
- Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA
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105
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Responsiveness of Trichomonas vaginalis to iron concentrations: Evidence for a post-transcriptional iron regulation by an IRE/IRP-like system. INFECTION GENETICS AND EVOLUTION 2009; 9:1065-74. [DOI: 10.1016/j.meegid.2009.06.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2009] [Revised: 05/28/2009] [Accepted: 06/08/2009] [Indexed: 01/06/2023]
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106
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Au C, Benedetto A, Anderson J, Labrousse A, Erikson K, Ewbank JJ, Aschner M. SMF-1, SMF-2 and SMF-3 DMT1 orthologues regulate and are regulated differentially by manganese levels in C. elegans. PLoS One 2009; 4:e7792. [PMID: 19924247 PMCID: PMC2773845 DOI: 10.1371/journal.pone.0007792] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2009] [Accepted: 10/09/2009] [Indexed: 11/19/2022] Open
Abstract
Manganese (Mn) is an essential metal that can exert toxic effects at high concentrations, eventually leading to Parkinsonism. A major transporter of Mn in mammals is the divalent-metal transporter (DMT1). We characterize here DMT1-like proteins in the nematode C. elegans, which regulate and are regulated by Mn and iron (Fe) content. We identified three new DMT1-like genes in C. elegans: smf-1, smf-2 and smf-3. All three can functionally substitute for loss of their yeast orthologues in S. cerevisiae. In the worm, deletion of smf-1 or smf-3 led to an increased Mn tolerance, while loss of smf-2 led to increased Mn sensitivity. smf mRNA levels measured by QRT-PCR were up-regulated upon low Mn and down-regulated upon high Mn exposures. Translational GFP-fusions revealed that SMF-1 and SMF-3 strongly localize to partially overlapping apical regions of the gut epithelium, suggesting a differential role for SMF-1 and SMF-3 in Mn nutritional intake. Conversely, SMF-2 was detected in the marginal pharyngeal epithelium, possibly involved in metal-sensing. Analysis of metal content upon Mn exposure in smf mutants revealed that SMF-3 is required for normal Mn uptake, while smf-1 was dispensable. Higher smf-2 mRNA levels correlated with higher Fe content, supporting a role for SMF-2 in Fe uptake. In smf-1 and smf-3 but not in smf-2 mutants, increased Mn exposure led to decreased Fe levels, suggesting that both metals compete for transport by SMF-2. Finally, SMF-3 was post-translationally and reversibly down-regulated following Mn-exposure. In sum, we unraveled a complex interplay of transcriptional and post-translational regulations of 3 DMT1-like transporters in two adjacent tissues, which regulate metal-content in C. elegans.
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Affiliation(s)
- Catherine Au
- Department of Pediatrics, Vanderbilt University, Nashville, Tennessee, United States of America
- Center for Molecular Toxicology, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Alexandre Benedetto
- Department of Pediatrics, Vanderbilt University, Nashville, Tennessee, United States of America
- Children's Hospital, Vanderbilt University, Nashville, Tennessee, United States of America
- London Centre for Nanotechnology, University College London, London, United Kingdom
| | - Joel Anderson
- Department of Nutrition, The University of North Carolina Greensboro, Greensboro, North Carolina, United States of America
| | - Arnaud Labrousse
- Centre d'Immunologie de Marseille-Luminy, Université de la Méditerranée, Marseille, France
- U631, INSERM, Marseille, France
- UMR6102, CNRS, Marseille, France
- Institut de Pharmacologie et de Biologie Structurale, Université Paul Sabatier Toulouse III, Toulouse, France
| | - Keith Erikson
- Department of Nutrition, The University of North Carolina Greensboro, Greensboro, North Carolina, United States of America
| | - Jonathan J. Ewbank
- Centre d'Immunologie de Marseille-Luminy, Université de la Méditerranée, Marseille, France
- U631, INSERM, Marseille, France
- UMR6102, CNRS, Marseille, France
| | - Michael Aschner
- Department of Pediatrics, Vanderbilt University, Nashville, Tennessee, United States of America
- Center for Molecular Toxicology, Vanderbilt University, Nashville, Tennessee, United States of America
- Children's Hospital, Vanderbilt University, Nashville, Tennessee, United States of America
- * E-mail:
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107
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Salahudeen AA, Bruick RK. Maintaining Mammalian iron and oxygen homeostasis: sensors, regulation, and cross-talk. Ann N Y Acad Sci 2009; 1177:30-8. [PMID: 19845604 DOI: 10.1111/j.1749-6632.2009.05038.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Though iron and oxygen are required to sustain essential biological processes, an excess of either can result in oxidative stress. Therefore, mammals tightly regulate cellular and systemic iron and oxygen homeostasis. At the cellular level, the hypoxia-inducible transcription factors (HIFs) are key mediators of oxygen homeostasis through their regulation of genes involved in anaerobic metabolism and oxygen delivery, among others. Iron regulatory proteins (IRPs) largely govern cellular iron homeostasis through their effects on the translation and stability of mRNAs involved in iron uptake, utilization, export, and storage. Here, we describe regulatory factors for each pathway that sense both iron and oxygen availability and coordinate the maintenance of mammalian iron and oxygen homeostasis at both the cellular and systemic levels.
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Affiliation(s)
- Ameen A Salahudeen
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390-903, USA
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108
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Khan MA, Walden WE, Goss DJ, Theil EC. Direct Fe2+ sensing by iron-responsive messenger RNA:repressor complexes weakens binding. J Biol Chem 2009; 284:30122-8. [PMID: 19720833 DOI: 10.1074/jbc.m109.041061] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fe(2+) is now shown to weaken binding between ferritin and mitochondrial aconitase messenger RNA noncoding regulatory structures ((iron-responsive element) (IRE)-RNAs) and the regulatory proteins (IRPs), which adds a direct role of iron to regulation that can complement the well known regulatory protein modification and degradative pathways related to iron-induced mRNA translation. We observe that the K(d) value increases 17-fold in 5'-untranslated region IRE-RNA:repressor complexes; Fe(2+), is studied in the absence of O(2). Other metal ions, Mn(2+) and Mg(2+) have similar effects to Fe(2+) but the required Mg(2+) concentration is 100 times greater than for Fe(2+) or Mn(2+). Metal ions also weaken ethidium bromide binding to IRE-RNA with no effect on IRP fluorescence, using Mn(2+) as an O(2)-resistant surrogate for Fe(2+), indicating that metal ions bound IRE-RNA but not IRP: Fe(2+) decreases IRP repressor complex stability of ferritin IRE-RNA 5-10 times compared with 2-5 times for mitochondrial aconitase IRE-RNA, over the same concentration range, suggesting that differences among IRE-RNA structures contribute to the differences in the iron responses observed in vivo. The results show the IRE-RNA:repressor complex literally responds to Fe(2+), selectively for each IRE-mRNA.
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Affiliation(s)
- Mateen A Khan
- Department of Chemistry, Hunter College, City University of New York, New York, New York 10065, USA
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109
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Abstract
By virtue of its unique electrochemical properties, iron makes an ideal redox active cofactor for many biologic processes. In addition to its important role in respiration, central metabolism, nitrogen fixation, and photosynthesis, iron also is used as a sensor of cellular redox status. Iron-based sensors incorporate Fe-S clusters, heme, and mononuclear iron sites to act as switches to control protein activity in response to changes in cellular redox balance. Here we provide an overview of iron-based redox sensor proteins, in both prokaryotes and eukaryotes, that have been characterized at the biochemical level. Although this review emphasizes redox sensors containing Fe-S clusters, proteins that use heme or novel iron sites also are discussed.
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Affiliation(s)
- F Wayne Outten
- Department of Chemistry and Biochemistry, The University of South Carolina, 631 Sumter Street, Columbia, South Carolina 29208, USA.
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110
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Cysteine oxidation regulates the RNA-binding activity of iron regulatory protein 2. Mol Cell Biol 2009; 29:2219-29. [PMID: 19223469 DOI: 10.1128/mcb.00004-09] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Iron regulatory protein 2 (IRP2) is an RNA-binding protein that regulates the posttranscriptional expression of proteins required for iron homeostasis such as ferritin and transferrin receptor 1. IRP2 RNA-binding activity is primarily regulated by iron-mediated proteasomal degradation, but studies have suggested that IRP2 RNA binding is also regulated by thiol oxidation. We generated a model of IRP2 bound to RNA and found that two cysteines (C512 and C516) are predicted to lie in the RNA-binding cleft. Site-directed mutagenesis and thiol modification show that, while IRP2 C512 and C516 do not directly interact with RNA, both cysteines are located within the RNA-binding cleft and must be unmodified/reduced for IRP2-RNA interactions. Oxidative stress induced by cellular glucose deprivation reduces the RNA-binding activity of IRP2 but not IRP2-C512S or IRP2-C516S, consistent with the formation of a disulfide bond between IRP2 C512 and C516 during oxidative stress. Decreased IRP2 RNA binding is correlated with reduced transferrin receptor 1 mRNA abundance. These studies provide insight into the structural basis for IRP2-RNA interactions and reveal an iron-independent mechanism for regulating iron homeostasis through the redox regulation of IRP2 cysteines.
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111
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Iron and the translation of the amyloid precursor protein (APP) and ferritin mRNAs: riboregulation against neural oxidative damage in Alzheimer's disease. Biochem Soc Trans 2009; 36:1282-7. [PMID: 19021541 DOI: 10.1042/bst0361282] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The essential metals iron, zinc and copper deposit near the Abeta (amyloid beta-peptide) plaques in the brain cortex of AD (Alzheimer's disease) patients. Plaque-associated iron and zinc are in neurotoxic excess at 1 mM concentrations. APP (amyloid precursor protein) is a single transmembrane metalloprotein cleaved to generate the 40-42-amino-acid Abetas, which exhibit metal-catalysed neurotoxicity. In health, ubiquitous APP is cleaved in a non-amyloidogenic pathway within its Abeta domain to release the neuroprotective APP ectodomain, APP(s). To adapt and counteract metal-catalysed oxidative stress, as during reperfusion from stroke, iron and cytokines induce the translation of both APP and ferritin (an iron storage protein) by similar mechanisms. We reported that APP was regulated at the translational level by active IL (interleukin)-1 (IL-1-responsive acute box) and IRE (iron-responsive element) RNA stem-loops in the 5' untranslated region of APP mRNA. The APP IRE is homologous with the canonical IRE RNA stem-loop that binds the iron regulatory proteins (IRP1 and IRP2) to control intracellular iron homoeostasis by modulating ferritin mRNA translation and transferrin receptor mRNA stability. The APP IRE interacts with IRP1 (cytoplasmic cis-aconitase), whereas the canonical H-ferritin IRE RNA stem-loop binds to IRP2 in neural cell lines, and in human brain cortex tissue and in human blood lysates. The same constellation of RNA-binding proteins [IRP1/IRP2/poly(C) binding protein] control ferritin and APP translation with implications for the biology of metals in AD.
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112
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Takaesu A, Watanabe K, Takai S, Sasaki Y, Orino K. Sequence analysis of dolphin ferritin H and L subunits and possible iron-dependent translational control of dolphin ferritin gene. Acta Vet Scand 2008; 50:42. [PMID: 18954429 PMCID: PMC2603009 DOI: 10.1186/1751-0147-50-42] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2008] [Accepted: 10/27/2008] [Indexed: 12/02/2022] Open
Abstract
Background Iron-storage protein, ferritin plays a central role in iron metabolism. Ferritin has dual function to store iron and segregate iron for protection of iron-catalyzed reactive oxygen species. Tissue ferritin is composed of two kinds of subunits (H: heavy chain or heart-type subunit; L: light chain or liver-type subunit). Ferritin gene expression is controlled at translational level in iron-dependent manner or at transcriptional level in iron-independent manner. However, sequencing analysis of marine mammalian ferritin subunits has not yet been performed fully. The purpose of this study is to reveal cDNA-derived amino acid sequences of cetacean ferritin H and L subunits, and demonstrate the possibility of expression of these subunits, especially H subunit, by iron. Methods Sequence analyses of cetacean ferritin H and L subunits were performed by direct sequencing of polymerase chain reaction (PCR) fragments from cDNAs generated via reverse transcription-PCR of leukocyte total RNA prepared from blood samples of six different dolphin species (Pseudorca crassidens, Lagenorhynchus obliquidens, Grampus griseus, Globicephala macrorhynchus, Tursiops truncatus, and Delphinapterus leucas). The putative iron-responsive element sequence in the 5'-untranslated region of the six different dolphin species was revealed by direct sequencing of PCR fragments obtained using leukocyte genomic DNA. Results Dolphin H and L subunits consist of 182 and 174 amino acids, respectively, and amino acid sequence identities of ferritin subunits among these dolphins are highly conserved (H: 99–100%, (99→98) ; L: 98–100%). The conserved 28 bp IRE sequence was located -144 bp upstream from the initiation codon in the six different dolphin species. Conclusion These results indicate that six different dolphin species have conserved ferritin sequences, and suggest that these genes are iron-dependently expressed.
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113
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Canzoneri JC, Oyelere AK. Interaction of anthracyclines with iron responsive element mRNAs. Nucleic Acids Res 2008; 36:6825-34. [PMID: 18953029 PMCID: PMC2588532 DOI: 10.1093/nar/gkn774] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Double-stranded sections of mRNA are often inviting sites of interaction for a wide variety of proteins and small molecules. Interactions at these sites can serve to regulate, or disrupt, the homeostasis of the encoded protein products. Such ligand target sites exist as hairpin-loop structures in the mRNAs of several of the proteins involved in iron homeostasis, including ferritin heavy and light chains, and are known as iron responsive elements (IREs). These IREs serve as the main control mechanism for iron metabolism in the cell via their interaction with the iron regulatory proteins (IRPs). Disruption of the IRE/IRP interaction could greatly affect iron metabolism. Here, we report that anthracyclines, a class of clinically useful chemotherapeutic drugs that includes doxorubicin and daunorubicin, specifically interact with the IREs of ferritin heavy and light chains. We characterized this interaction through UV melting, fluorescence quenching and drug-RNA footprinting. Results from footprinting experiments with wild-type and mutant IREs indicate that anthracyclines preferentially bind within the UG wobble pairs flanking an asymmetrically bulged C-residue, a conserved base that is essential for IRE-IRP interaction. Additionally, drug-RNA affinities (apparent K(d)s) in the high nanomolar range were calculated from fluorescence quenching experiments, while UV melting studies revealed shifts in melting temperature (DeltaT(m)) as large as 10 degrees C. This anthracycline-IRE interaction may contribute to the aberration of intracellular iron homeostasis that results from anthracycline exposure.
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Affiliation(s)
- Joshua C Canzoneri
- School of Chemistry and Biochemistry, Parker H Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
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114
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dos Santos CO, Dore LC, Valentine E, Shelat SG, Hardison RC, Ghosh M, Wang W, Eisenstein RS, Costa FF, Weiss MJ. An iron responsive element-like stem-loop regulates alpha-hemoglobin-stabilizing protein mRNA. J Biol Chem 2008; 283:26956-64. [PMID: 18676996 DOI: 10.1074/jbc.m802421200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Hemoglobin production during erythropoiesis is mechanistically coupled to the acquisition and metabolism of iron. We discovered that iron regulates the expression of alpha-hemoglobin-stabilizing protein (AHSP), a molecular chaperone that binds and stabilizes free alpha-globin during hemoglobin synthesis. In primates, the 3'-untranslated region (UTR) of AHSP mRNA contains a nucleotide sequence resembling iron responsive elements (IREs), stem-loop structures that regulate gene expression post-transcriptionally by binding iron regulatory proteins (IRPs). The AHSP IRE-like stem-loop deviates from classical consensus sequences and binds IRPs poorly in electrophoretic mobility shift assays. However, in cytoplasmic extracts, AHSP mRNA co-immunoprecipitates with IRPs in a fashion that is dependent on the stem-loop structure and inhibited by iron. Moreover, this interaction enhances AHSP mRNA stability in erythroid and heterologous cells. Our findings demonstrate that IRPs can regulate mRNA expression through non-canonical IREs and extend the repertoire of known iron-regulated genes. In addition, we illustrate a new mechanism through which hemoglobin may be modulated according to iron status.
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Affiliation(s)
- Camila O dos Santos
- Division of Hematology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, USA
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115
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Isolation and characterization of the iron-binding properties of a primitive monolobal transferrin from Ciona intestinalis. J Biol Inorg Chem 2008; 13:873-85. [DOI: 10.1007/s00775-008-0375-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2008] [Accepted: 04/04/2008] [Indexed: 11/25/2022]
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116
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Volz K. The functional duality of iron regulatory protein 1. Curr Opin Struct Biol 2008; 18:106-11. [PMID: 18261896 DOI: 10.1016/j.sbi.2007.12.010] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2007] [Revised: 12/16/2007] [Accepted: 12/17/2007] [Indexed: 12/13/2022]
Abstract
Iron homeostasis in animal cells is controlled post-transcriptionally by the iron regulatory proteins IRP1 and IRP2. IRP1 can assume two different functions in the cell, depending on conditions. During iron scarcity or oxidative stress, IRP1 binds to mRNA stem-loop structures called iron responsive elements (IREs) to modulate the translation of iron metabolism genes. In iron-rich conditions, IRP1 binds an iron-sulfur cluster to function as a cytosolic aconitase. This functional duality of IRP1 connects the translational control of iron metabolizing proteins to cellular iron levels. The recently determined structures of IRP1 in both functional states reveal the large-scale conformational changes required for these mutually exclusive roles, providing new insights into the mechanisms of IRP1 interconversion and ligand binding.
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Affiliation(s)
- Karl Volz
- Department of Microbiology and Immunology, University of Illinois at Chicago, Chicago, IL 60612-7344, USA.
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117
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Wang J, Chen G, Lee J, Pantopoulos K. Iron-dependent degradation of IRP2 requires its C-terminal region and IRP structural integrity. BMC Mol Biol 2008; 9:15. [PMID: 18226225 PMCID: PMC2267205 DOI: 10.1186/1471-2199-9-15] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2007] [Accepted: 01/28/2008] [Indexed: 01/08/2023] Open
Abstract
Background Iron regulatory protein 2 (IRP2), a post-transcriptional regulator of cellular iron metabolism, undergoes iron-dependent degradation via the ubiquitin-proteasome pathway. A stretch of 73 amino acids within the N-terminal domain 1 of the protein was reported to function as an iron sensor. However, mutants lacking this fragment remain sensitive to degradation in iron-replete cells. Results To identify elements within IRP2 involved in the control of its stability, we undertook a systematic mutagenesis approach. Truncated versions of IRP2 were expressed in H1299 cells and analyzed for their response to iron. Deletion mutants lacking the entire C-terminal domain 4 (amino acids 719–963) of IRP2 remained stable following iron treatments. Moreover, the replacement of domain 4 of IRP1 with the corresponding region of IRP2 sensitized the chimerical IRP11–3/IRP24 protein to iron-dependent degradation, while the reverse manipulation gave rise to a stable chimerical IRP21–3/IRP14 protein. The deletion of just 26 or 34 C-terminal amino acids stabilized IRP2 against iron. However, the fusion of C-terminal IRP2 fragments to luciferase failed to sensitize the indicator protein for degradation in iron-loaded cells. Conclusion Our data suggest that the C-terminus of IRP2 contains elements that are necessary but not sufficient for iron-dependent degradation. The functionality of these elements depends upon the overall IRP structure.
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Affiliation(s)
- Jian Wang
- Lady Davis Institute for Medical Research, Sir Mortimer B, Davis Jewish General Hospital, Montreal, Quebec, Canada.
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Jung SH, DeRuisseau LR, Kavazis AN, DeRuisseau KC. Plantaris muscle of aged rats demonstrates iron accumulation and altered expression of iron regulation proteins. Exp Physiol 2007; 93:407-14. [DOI: 10.1113/expphysiol.2007.039453] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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119
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Cellier MF, Courville P, Campion C. Nramp1 phagocyte intracellular metal withdrawal defense. Microbes Infect 2007; 9:1662-70. [PMID: 18024118 DOI: 10.1016/j.micinf.2007.09.006] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Natural resistance-associated macrophage proteins (Nramp) are multispecific symporters facilitating proton-dependent import of divalent metals. Nramp1 restricts microbial access to essential micro-nutrients such as iron and manganese within professional phagosomes. Increased understanding of Nramp1 roles in human phagocytes will be useful for future therapeutic approaches against selected infectious and immune diseases.
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Affiliation(s)
- Mathieu F Cellier
- INRS-Institut Armand-Frappier, 531, Bd des prairies, Laval, Québec H7V 1B7, Canada.
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